Multi-frequency antenna

Abstract

A multi-frequency antenna includes a first antenna element, a second antenna element, a connection element, a third antenna element and a shorted element. The connection element is connected between the first antenna element and a neighborhood portion of the third antenna element. A feeding point is located in or nearby a first junction between the connection element and the first antenna element or located in the connection element. The shorted element is connected between the second antenna element and the grounding plane. The shorted element extends from a second junction between the second antenna element and the third antenna element to the grounding plane. The first conductive path that extends from the feeding point to the other end of the shorted element is substantially equal to a second conductive length that extends from the feeding point to the free end of the first antenna element.

What is claimed is: 
     
       1. A multi-frequency antenna comprising:
 a first antenna element for operating at a first frequency band and defining two ends, wherein one end of said first antenna element is a free end; 
 a connection element, one end of said connection element connected to the other end of said first antenna element, wherein a coaxial cable has an inner connector connected to a feeding point and an outer conductor connected to a grounding plane, wherein said feeding point is located in or nearby a first junction between said connection element and said first antenna element; 
 a second antenna element for operating at a second frequency band; 
 a third antenna element for operating at a third frequency band, wherein the other end of said connection element is connected to a neighborhood portion of said third antenna element; and 
 a shorted element connected between said second antenna element and said grounding plane, wherein one end of said shorted element extends from a second junction between said second antenna element and said third antenna element and a first conductive path that extends from said feeding point to the other end of said shorted element is substantially equal to a second conductive length that extends from said feeding point to said free end of said first antenna element. 
 
     
     
       2. The multi-frequency antenna as claimed in  claim 1 , wherein the first antenna element has a serpentine shape. 
     
     
       3. The multi-frequency antenna as claimed in  claim 1 , wherein a distance between said feeding point and said free end of said first antenna element is substantially a quarter of a wavelength corresponding to a central frequency of said first frequency band. 
     
     
       4. The multi-frequency antenna as claimed in  claim 1 , wherein a part of the third antenna element is a inverted-L shape extending from said connection element toward a side where said second antenna element is located, such that a concave space is formed between said third antenna element and said second antenna element. 
     
     
       5. The multi-frequency antenna as claimed in  claim 1 , wherein said connection element is formed as a first strip, and said third antenna element and said second antenna element are formed as a second strip. 
     
     
       6. The multi-frequency antenna as claimed in  claim 1 , wherein said shorted element has at least one cross segment parallel to said second antenna element and at least one vertical segments parallel to said connection element. 
     
     
       7. The multi-frequency antenna as claimed in  claim 1 , wherein said first antenna element and said third antenna element are located in left side of said connection element, and said second antenna element is located in right side of said connection element. 
     
     
       8. The multi-frequency antenna as claimed in  claim 1 , wherein said first antenna element and said third antenna element lie in a transverse direction and said second antenna element lies in an opposite direction relative to said transverse direction. 
     
     
       9. The multi-frequency antenna as claimed in  claim 8 , wherein said connection element lies in a vertical direction perpendicular to said transverse direction. 
     
     
       10. The multi-frequency antenna as claimed in  claim 1 , wherein the central frequency of said first frequency band is nearby the central frequency of said second frequency band such that a first band is composed of the bandwidth of said first frequency band and that of said second frequency band, and said second band is the bandwidth of said third frequency band. 
     
     
       11. A multi-frequency antenna comprising:
 a first antenna element for operating at a first frequency band and defining two ends, wherein one end of said first antenna element is a free end; 
 a connection element connected to the other end of said first antenna element, wherein a coaxial cable has an inner connector connected to a feeding point and an outer conductor connected to a grounding plane, wherein said feeding point is located in said connection element; 
 a second antenna element for operating at a second frequency band; 
 a third antenna element for operating at a third frequency band, wherein the other end of said connection element is connected to a neighborhood portion of said third antenna element; and 
 a shorted element connected between said second antenna element and said grounding plane, wherein one end of said shorted element extends from a second junction between said second antenna element and said third antenna element and a first conductive path that extends from said feeding point to the other end of said shorted element is substantially equal to a second conductive length that extends from said feeding point to said free end of said first antenna element. 
 
     
     
       12. The multi-frequency antenna as claimed in  claim 11 , wherein the first antenna element has a serpentine shape. 
     
     
       13. The multi-frequency antenna as claimed in  claim 11 , wherein a distance between said feeding point and said free end of said first antenna element is substantially a quarter of a wavelength corresponding to a central frequency of said first frequency band. 
     
     
       14. The multi-frequency antenna as claimed in  claim 11 , wherein a part of the third antenna element is a inverted-L shape extending from said connection element toward a side where said second antenna element is located, such that a concave space is formed between said third antenna element and said second antenna element. 
     
     
       15. The multi-frequency antenna as claimed in  claim 11 , wherein said connection element is formed as a first strip, and said third antenna element and said second antenna element are formed as a second strip. 
     
     
       16. The multi-frequency antenna as claimed in  claim 11 , wherein said shorted element has at least one cross segment parallel to said second antenna element and said shorted element has at least one vertical segments parallel to said connection element. 
     
     
       17. The multi-frequency antenna as claimed in  claim 11 , wherein said first antenna element and said third antenna element are located in the left side of said connection element, and said second antenna element is located in the right side of said connection element. 
     
     
       18. The multi-frequency antenna as claimed in  claim 11 , wherein said first antenna element and said third antenna element lie in a transverse direction and said second antenna element lies in an opposite direction relative to said transverse direction. 
     
     
       19. The multi-frequency antenna as claimed in  claim 18 , wherein said connection element lies in a vertical direction perpendicular to said transverse direction. 
     
     
       20. The multi-frequency antenna as claimed in  claim 11 , wherein the central frequency of said first frequency band is nearby the central frequency of said second frequency band such that a first band is composed of the bandwidth of said first frequency band and that of said second frequency band, and said second band is the bandwidth of said third frequency band.